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Update: Serologic Testing for HIV-1 Antibody --United States, 1988 and 1989

In 1985, the first enzyme immunoassay (EIA) for detection of human immunodeficiency virus type 1 (HIV-1) antibody was licensed by the Food and Drug Administration; since then, the number of HIV-1 tests performed and the number of laboratories performing HIV-1 tests has increased steadily. Because of the need to assess the quality of existing laboratory technology and to ensure the quality of testing, the Model Performance Evaluation Program (MPEP) was implemented by CDC in 1986 to evaluate the performance of laboratories testing for HIV-1 infection (1). Approximately 1400 U.S. and international laboratories participated in the MPEP during 1988 and 1989. The total number of laboratories performing HIV-1 testing is unknown. Laboratories in the MPEP voluntarily report results from coded plasma samples for which HIV-1-antibody reactivity has been determined through composite testing at CDC and verified at candidate reference laboratories (Table 1). Participants also complete survey forms describing laboratory characteristics and testing practices. This report summarizes data for the 752 U.S. MPEP laboratories that returned complete results in both May 1988 and August 1989*. Performance is described in terms of analytic sensitivity, analytic specificity, and overall analytic performance.** Performance was calculated based on a laboratory's test results for samples that were typical of most samples routinely tested for HIV-1 antibody. Enzyme Immunoassays The analytic sensitivity of EIAs for HIV-1 antibody performed for MPEP in 1988 was 99.7% (6545 reactive test results out of 6566 positive samples) (Table 2); analytic specificity was 98.5% (3004 nonreactive test results out of 3051 negative samples). The overall analytic performance of EIAs was 99.3% (9549 correct results out of 9617 tests). Laboratories performing HIV-1-antibody tests were classified into 15 laboratory types. Five types of laboratories accounted for 709 (94.7%) of the 749 MPEP laboratories performing EIAs: non-blood-bank hospital (241 (32.2%)), laboratories identifying themselves as independent (140 (18.7%)), hospital blood bank (124 (16.6%)), nonhospital blood bank (122 (16.3%)), and health department (82 (10.9%)). For EIAs performed in 1988, laboratory type-specific analytic sensitivity among the major laboratory types ranged from 99.3% to 100.0%; analytic specificity, from 98.1% to 99.5%; and overall analytic performance, from 98.9% to 99.8%. Non-blood-bank hospital laboratories reported the largest percentages of EIA results in both 1988 and 1989 (2868 (29.8%) of 9617 results in 1988 and 2372 (29.0%) of 8190 results in 1989). However, the percentages of EIA results reported on MPEP samples decreased from 1988 to 1989 for both non-blood-bank hospital and hospital blood bank laboratories (from 1488 (15.5%) in 1988 to 1247 (15.2%) in 1989 for hospital blood bank laboratories). The percentages of EIA results reported increased in independent (from 18.4% to 18.6%), nonhospital blood bank (from 17.7% to 17.9%), health department (from 12.5% to 13.0%), and other types of laboratories (from 6.0% to 6.3%). Health department and other types of laboratories had the largest distribution increases (4.0% and 5.0%, respectively). Western Blot In 1988, the analytic sensitivity for Western blot (WB) tests*** performed for MPEP was 99.3% (1345 reactive test results out of 1355 positive samples); analytic specificity was 91.6% (306 nonreactive test results out of 334 negative samples) (Table 2). Overall analytic performance of WB in 1988 was 97.8% (1651 correct results out of 1689 tests). Analytic sensitivity, analytic specificity, and overall analytic performance were similar for WBs performed with licensed and unlicensed test kits. Four types of laboratories accounted for 115 (82.1%) of the 140 laboratories performing WB tests in 1988: health department (41 (29.3%)), independent (27 (19.3%)), non-blood-bank hospital (27 (19.3%)), and nonhospital blood bank (20 (14.3%)). For WBs performed in 1988, laboratory type-specific analytic sensitivity among the major laboratory types ranged from 98.7% to 100.0%; analytic specificity, from 85.0% to 98.7%; and overall analytic performance, from 96.2% to 99.1%. In 1989, analytic specificity for WB tests was 97.8% (364 nonreactive test results out of 372 negative samples)--a 6.8% increase over specificity in 1988 (Table 2). In 1989, 159 (21.1%) MPEP laboratories performed WBs, an increase of 13.6% over the number in 1988. Four types of laboratories continued to report most WB results on MPEP samples and accounted for 129 (81.1%) of the laboratories performing WBs: health department (47 (29.6%)), independent (33 (20.8%)), non-blood-bank hospital (31 (19.5%)), and nonhospital blood bank (18 (11.3%)). The percentages of WB results reported from the two largest categories of WB laboratories (health department and independent) increased from 1988 to 1989 (from 453 (26.8%) of 1689 results in 1988 to 246 (27.3%) of 900 results in 1989 for health department and from 349 (20.7%) in 1988 to 204 (22.7%) in 1989 for independent). In nonhospital blood bank and other types of laboratories, the percentages of WB results reported decreased (from 16.9% to 14.7% for nonhospital blood bank and from 17.5% to 16.6% for other laboratories). For WBs performed in 1989, laboratory type-specific analytic sensitivity among the major laboratory types ranged from 97.1% to 100.0%; analytic specificity, from 96.0% to 100.0%; and overall analytic performance, from 97.1% to 99.2%. Reported by: Div of Laboratory Systems, Public Health Practice Program Office, CDC.

Editorial Note

Editorial Note: Assuring accurate results in tests for HIV-1 antibody remains a critical component of surveillance for HIV-1 infections. Results from proficiency testing programs can measure the operational performance of participating laboratories but must be interpreted cautiously. HIV-1 proficiency testing programs rarely use fresh single-donor specimens from persons who may or may not be infected with HIV-1. Because of the necessity to use large volumes of sample materials, proficiency testing programs often use pooled human plasma samples and dilutions of single reactive plasma samples in HIV-1-antibody-negative serum. These samples may react nonspecifically and may be difficult to test and interpret. Despite limitations, proficiency testing is capable of identifying problems with particular types of samples, with particular tests, with reagents of kit manufacturers (2), and with interpretations and reporting of testing results (3). Proficiency testing can also serve as a valuable education tool. The MPEP incorporates useful elements of proficiency testing programs but also contains features, such as frequently using single-donor undiluted plasma for sam ples, that avoid some of the problems encountered by proficiency testing programs. By using survey data, the MPEP can evaluate parameters such as analytic sensitivity and analytic specificity for particular HIV-1 tests along with laboratory characteristics such as laboratory type. EIAs have proven valuable for screening donated blood for HIV-1 antibody to reduce HIV-1 transmission through blood transfusions and administration of clotting factors. In addition, an EIA is usually the first step in diagnosing HIV-1 infection. Thus, maintaining high analytic sensitivity of EIAs is important. WBs are frequently used as the independent supplemental test of higher specificity to confirm HIV-1 antibody following repeatedly reactive EIA test results. Possible reasons for increases in analytic specificity for WBs include improvements in the intrinsic properties of available tests, increased use of more standardized test methods, increased experience and training in the use of WBs by laboratory personnel, and increased use of more standardized interpretive criteria for test results. The Public Health Service endorsed the WB interpretive criteria for HIV-1 antibody in public health and clinical practice in July 1989 (4), within one month of the 1989 sample panel evaluation. Continued monitoring of performance data is important to assure quality performance of HIV-1-antibody tests, particularly if HIV-1 testing trends continue and testing capabilities and sophistication expand in both the private and public health sectors.

References

  1. Taylor RN, Przybyszewski VA. Summary of the Centers for Disease Control human immuno deficiency virus (HIV) performance evaluation surveys for 1985 and 1986. Am J Clin Pathol 1988;89:1-13.

  2. Polesky HF, Hanson MR. Human immunodeficiency virus type 1 proficiency testing: the American Association of Blood Banks/College of American Pathologists program. Arch Pathol Lab Med 1990;114:268-71.

  3. Benenson AS, Peddecord KM, Hofherr LK, Ascher MS, Taylor RN, Hearn TL. Reporting the results of human immunodeficiency virus testing. JAMA 1989;262:3435-8.

  4. CDC. Interpretation and use of the Western blot assay for serodiagnosis of human immuno deficiency virus type 1 infections. MMWR 1989;38(no. S-7).

    • Provisional data for 1989. ** Analytic sensitivity is the proportion of reactive test results in positive specimens. To cal culate analytic sensitivity, Western blot (WB) "indeterminate" test results are combined with nonreactive test results. Analytic specificity is the proportion of nonreactive test results in negative specimens. To calculate analytic specificity, WB "indeterminate" test results are combined with reactive test results. Overall analytic performance is the proportion of "correct" test results in all specimens tested. Because seroreactivity of included samples was defined as positive or negative, WB "indeterminate" test results are not considered "correct" for calculating overall analytic performance. *** WBs were performed with both the licensed test kit available in the United States and with laboratories' own WB test reagents using viral antigen purchased from commercial sources.



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